A fuel injection valve in a direct injection internal combustion engine is exposed to combustion gas of a high temperature because it is installed in the interior of the engine. Therefore, for example carbon resulting from fuel combustion is apt to be deposited at a tip portion of the fuel injection valve. Foreign matters such as oil, additives and water are mixed in fuel and are deposited in the fuel injecting portion during operation of the engine. Such deposited foreign matters are called deposits. Once deposits are formed in the fuel injecting portion, there arises the problem that highly accurate fuel injection can no longer be effected no matter high accurately the fuel injection valve may be constructed.
Particularly, in the case of a fuel injection valve having plural orifices, the deposits become more influential because the orifices are small.
In view of this point, for example in Japanese Patent Laid Open No. Hei 10 (1998)-159688 (Patent Document 1), a volatile film is formed on an orifice surface with a surface roughness of Rz 1 micron or less to improve the deposits suppressing effect.
On the other hand, as a method for machining a plurality of deflected orifices in a nozzle there is known an electric discharge machining method which is disclosed in Japanese Patent Laid Open No. 2006-272484 (Patent Document 2). According to the machining method for deflected fine holes (orifices) which method is disclosed in Patent Document 2, prepared holes are formed in a workpiece beforehand by laser beam machining and are established their positions by image processing, thereafter, fine holes are formed by electric discharge machining.